RESPIRATION 



135 



quantities of the nitrogen in the air of the lungs leak into the blood, from 

 which the gas is liberated in the form of bubbles when the pressure is 

 suddenly decreased as the caisson is pulled up. (Cf. the carbon dioxide 

 bubbles in soda-water bottles when the stopper is taken off.) However, if 

 the caisson is hauled up very slowly, the dissolved nitrogen in the blood 

 has a chance of re-entering the lungs, and there are no adverse effects. 



Now, though whales surface very quickly from great depths, no cases 

 of caisson sickness have been reported, and scientists have wondered why. 

 A number of improbable hypotheses were put forward JDcfore the simple 

 and obvious solution became generally accepted. Thus, in 1934, Nature, 

 the British journal devoted to the natural sciences, gave much space to the 

 discussion of this problem. One author thought that Cetacean lungs became 

 filled with water at great depths, another that all the air was expelled, and 

 a third that the blood circulation to the lungs was cut off. In 1933, Laurie, 

 investigating the blood of whales aboard a whaler, discovered the presence 

 of bacteria which, he thought, could absorb nitrogen, and which he called 

 micro-organisms X. Only two years later, however, he changed his mind 

 and admitted that 'organisms X' were nothing but putrifying agents 

 which do not occur in living whales. Speculation would have remained 

 rife, had not L. Hill (1935) shown that there is a basic difference between 

 diving inside a caisson and diving straight into the water. In a caisson, 

 there is a continuous supply of fresh air and thus 

 also of fresh nitrogen with which the blood 

 can become saturated, while the normal diver 

 takes down a fixed quantity of air so that, despite 

 the high pressure of the water, only a small 

 quantity of nitrogen is available for solution in 

 the blood. The experimental proof of this simple 

 hypothesis was given by Scholander, using frogs 

 (Fig. 76) . Two frogs were placed into a vessel of 

 water under a pressure of three atmospheres. 

 While one frog was supplied with air, the other 

 was not. When the pressure was suddenly de- 

 creased, the first frog showed clear signs of caisson 

 sickness, and the other Ijehaved quite normally. 



While we are on the subject of respiration, we 

 would do well to take a closer look at the kmss 



Figure y6. Two frogs in a vessel under high pressure. The 

 frog at the bottom does not suffer caisson effects, while the 

 frog on top does, when pressure is released. 



